Intravenous administration of substantial quantities of liquids including water, electrolytes, sugar, blood, pharmaceuticals, and various nutritional materials are commonly administered to hospitalized patients from a glass or plastic container using a plastic tubing conduit which terminates in a needle that is inserted into a superficial vein or artery. A patient's movements, however, may cause the tip of the needle to pierce the vascular wall and cause the liquid being administered to flow in the perivascular tissues. The liquid may accumulate and cause discoloration, discomfort and possible destruction of tissues, while precluding absorption into the metabolic pool of the materials being administered at the selected rate.
Prior liquid infusion infiltration detection apparatus and method (see, for example, U.S. Pat. No. 3,618,602) permitted the early detection of liquid infiltrations so that corrective actions could be promptly instituted. In such prior apparatus and method, the skin temperature in the region overlying the tip of the intravascular needle was continuously monitored. Since liquids administered to a patient are at room temperature or refrigerated, they are typically at a lower temperature than normal skin temperature. Thus, any undesirable perivascular accumulation of administered liquid produces a decrement in skin temperature in the region overlying the accumulation. Since the temperatures of hospital rooms are typically about 20.degree. C.-25.degree. C. and normal skin temperature is typically about 33.degree. C., a significant temperature difference commonly exists between infusion liquid and skin temperature to produce the change in skin temperature that signals the occurrence of an infiltration. However, it has been found in patients who are in a state of shock or who are undergoing, or have recently undergone, substantial surgery or anesthesia and in some small number of other patients, blood flow to the skin may be sufficiently reduced that the patient's skin temperature tends to approximate the ambient temperature. Under these conditions, a substantial difference between skin temperature and the temperature of the liquid being infused is not available to produce a substantial change in the temperature of the skin in a region thereof where perivascular infiltration of the infused liquid occurs. Also, in some circumstances (especially in tropical climates), hospital room temperatures may be elevated to levels approximating normal skin temperatures. Under these circumstances, a substantial temperature difference between skin temperature and the temperature of the liquid being infused is again not available to produce a substantial change in the temperature of the skin in a region thereof where perivascular infiltration of the infused liquid occurs.